In routine clinical radiology application, X-ray film is housed within a hinged "clam shell" cassette prior to, during and after exposure. The exposed X-ray film is then removed from the cassette in a dark room environment and photographically developed for subsequent reading and interpretation by the radiologist or other practitioner.
The typical radiological cassette comprises a hinged rigid plastic outer shell having two intensifying screens positioned therewith. When inserted into the cassette, the film is sandwiched between the two intensifying screens therewithin so as to allow the emulsion on either side of the film to be exclusively exposed to light from its contiguous screen. The cassette into which the intensifying screens are mounted provides a light-tight container for the X-ray film and also serves to hold the film in tight contact with the screens over its entire surface. The X-ray film is inserted into the cassette in the darkroom with the film subsequently being exposed during a patient exam and then removed for processing. As can be appreciated, careful handling of the cassette prolongs its life which is desirable in that cassettes typically have a minimum cost of approximately $300.
Intensifying screens are used in the cassette since they decrease the X-ray dose to the patient, while still affording a properly exposed X-ray film. Also, the reduction in exposure allows use of short exposure times, which becomes important when it is necessary to minimize patient motion. During X-ray exposure, the intensifying screen functions to absorb the energy in the X-ray beam that has penetrated the patient, and to convert this energy into a light pattern that has substantially the same information as the original X-ray beam. The light then forms a latent image on the X-ray film. As will be recognized, the transfer of information from the X-ray beam to the screen light to the film results in some loss of the information. Though in the prior art there are X-ray cassettes which incorporate only a single intensifying screen, the inclusion of two intensifying screens in the X-ray cassette allows either side of the X-ray film sandwiched therebetween to be exposed.
Each intensifying screen disposed in the X-ray cassette typically includes four layers and has a total thickness of about 15 or 16 mils. The base or screen support is generally made of a high-grade cardboard or of a polyester plastic, having a thickness of 7-10 mils. Applied to one planar surface of the base is a reflecting coat which is made of a white substance, such as titanium dioxide (TiO.sub.2), which is spread over the base in a thin layer of approximately 1 mil thickness. Though some screens do not have a reflecting layer, such a reflecting layer is usually incorporated into the screen. Since many light photons are directed toward the back of the screen, i.e. toward the base layer, and would be lost as far as photographic activity is concerned, the reflecting layer acts to reflect light back toward the front of the screen.
Applied directly over the reflecting coat or the base (if no reflecting coat is included) is a phosphor layer containing phosphor crystals. The crystals are suspended in a plastic (polymer) containing a substance to keep the plastic flexible. The thickness of the phosphor layer is typically about 4 mils for par speed screens with the thickness being increased 1 or 2 mils in high speed screens and being decreased slightly in detail screens. Finally, applied over the phosphor layer is a protective layer which is made of a plastic, largely composed of a cellulose compound that is mixed with other polymers. The layer is generally about 0.7 to 0.8 mils thick and is often made of methylcellulose. The protective layer generally serves three functions, i.e. to prevent static electricity, to give physical protection to the delicate phosphor layer, and to provide a surface that can be cleaned without damaging the phosphor layer.
One of the difficulties associated with cassette technology is the constant exposure of the upper-most layer of the intensifying screen, i.e. the protective methylcellulose layer (routinely called the "screen"), to dust and particulate contaminants in the dark room. Static charges which form over the surface of the intensifying screen may cause dust, lint or other particulate matter to stick to the intensifying screen and to cause the appearance of artifactual images on the X-ray.
As can be appreciated, the intensifying screens and particularly the protective layer, must be kept clean in that any foreign material on the screen, such as paper, blood, dust, lint or static charges will block light photons and produce an area of underexposure on the X-ray film (typically referred to as "artifacts") corresponding to the size and shape of the soiled area. Though the cleaning of the protective layer reduces or eliminates the "artifacts" thereon, such cleanings are a major source of "screen" wear. Since quality assurance is becoming an essential feature of radiography, the particular shadows of the various screen "artifacts" previously described are no longer accepted when they appear on the final film. Should an "artifact" be seen and the "screen" recleaned, the patient must be re-exposed to the X-ray which causes both a delay in the patient care and an unnecessary increase in the total X-ray dose to the patient.
Though maintaining the cleanliness of the screen is desirable, as previously specified, the repeated cleaning of the "screen" wears down the protective layer and shortens its life. In this respect, the primary cause of screen failure is mechanical attrition. Under normal conditions of use, X-ray photons will not damage the screen, though such damage frequently occurs on the basis of continued cleanings. For many years, major manufacturers of X-ray cassettes have sold products referred to as "intensifying screen cleaners" which are typically provided in squirt bottle dispensers that contain an anti-static compound and a detergent. The instructions accompanying at least one of these cleaners generally recommend that the cleaning solution be applied to the surface of the screen with a gauze pad. However, the current use of gauze pads in relation to cleaning screens gives rise to undesirable effects in that the woven surface of the pad is made to absorb and not to clean. The frequent use of a gauze pad for this purpose may cause undue wear or erosion of the intensifying screen surface. Additionally, visible streaking occurs when a fluid is wiped over a polymer surface using such a pad. The woven, cotton gauze may further create lint such lint being a major cause of subsequent screen artifacts appearing on X-ray films. Finally, the abrasive nature of the gauze pad shortens the screen life. In addition to the aforementioned shortcomings, the gauze pads are typically expensive in that they are often packaged as individual sterile items in individual paper pouches. A clean gauze pad is required for screen cleaning, but sterility is an unnecessary expense. Further, the tearing open of the paper pack may in itself, create dust, which such dust may result in screen artifacts on the subsequent X-ray exposure.
As previously indicated, the protective layer of the intensifying screen must be cleaned on a daily basis to minimize lint, particulate matter, dust and static electricity since each of these elements, in addition to paper, can create artifacts on the final film product. The sterile gauze wipes currently utilized to clean the screens are an unexpected source of particulate contamination and static electricity, and also contribute to mechanical wear of the screen. Thus, the need to frequently rewash the screens actually shortens screen life. The present invention overcomes these and other deficiencies associated with prior art screen cleaning methods by providing a kit for cleaning an X-ray intensifying screen which does not create screen artifacts and does not promote screen wear.